1. Field of the Invention
The present invention relates to integrated circuits, and particularly relates to reducing the relative stress between a passivation layer and a high density plasma layer that is formed with a high density plasma.
2. Description of the Prior Art
In the fabrication of an integrated circuit (IC) that comprises a substrate and at least a set of interconnects, a passivation layer is formed over the entire top surface of the substrate. This is an insulating, protective layer that prevents mechanical and chemical damage during assembly and packaging.
In general, the passivation layer must satisfy the following desired properties:
(1) Provide good scratch protection to underlying structures.
(2) Be impermeable to moisture.
(3) Exhibit low stress.
(4) Provide conformal step coverage.
(5) Demonstrate high thickness uniformity.
(6) Be impermeable to sodium atoms and other high mobile impurities.
(7) Be easily patterned.
(8) Demonstrate good adhesion to conductor.
A serious defect of the passivation layer is a result of the passivation layer being broadly formed by chemical vapor deposition (CVD) process in contemporary techniques. Therefore, the coverage ability of the CVD induces a disadvantage that adjacent conductive lines on the top surface of the integrated circuit may not be properly isolated by the passivation layer, which is more serious when integration of the integrated circuit is increased.
FIG. 1 shows a rough illustration of a cross-section view of an integrated circuit with some disadvantages. Isolation 11, gate 12, spacer 13, source 14 and drain 15 are located in and on substrate 10. Besides, interconnects 16, contacts 17 and dielectric layers 18 are formed on substrate to provide required metallization structure. Additionally, conductive lines 19 are formed on the metallization structure and affected as interconnects. Therefore, when passivation layer 193 is formed on the metallization structure by CVD, owing to the coverage of CVD, it is possible that void 196 is formed between two adjacent conductive lines 19 and increases the risk that adjacent conductive lines 19 are not properly isolated.
A well-known method which is broadly applied in the fabrication of the integrated circuit having a critical dimension less than 0.5 xcexcm to overcome the previous disadvantage to to form passivation layer 196 that directly covers conductive lines 19 by CVD with a high density plasma, as shown in FIG. 2. Characteristic of the method is that during deposition, a DC bias is applied on the wafer and then particles of plasma such as Ar will collide the deposited high density plasma layer 195. Therefore, owing to the fact that colliding frequency is proportional to the electric field and the field is larger in edges of high density plasma layer 195, hinges of high density plasma layer 195 are eliminated by collision and then no void is formed. Incidentally, owing to the fact the colliding frequency is larger in the edge and is smaller in the top, the thickness of high density plasma layer 195 is not uniform even if it covers a smooth surface.
Nevertheless, high density plasma layer 195 cannot properly protect against permeation of wafer and gas. An improved method is provided wherein passivation layer 193 is formed on high density plasma layer 195 to improve the quality of passivation of the integrated circuit. In other words, an integrated circuit is protected by a complex passivation layer that is formed by HDP and deposition in sequence.
However, an inevitable disadvantage of the improved method is that the absolute value of relative stress between high density plasma layer 195 and passivation layer 193 is about 1.8E08 dynes/cm2, such a high relative stress increases the risk that passivation of integrated circuit is degraded by cracks and pealing of passivation. FIG. 3 shows the possible result of high relative stress. Where there are a plurality of cracks and pealing in passivation layer 193, and other parts of the integrated circuit are omitted.
Therefore, it is indisputable that development of a new structure of passivation to overcome the disadvantage of high relative stress is desired, and the new structure of passivation is more important as high density plasma layer 195 is irreplaceable.
It is an object of the invention to propose some structures that efficiently prevent cracking and pealing which are induced by high relative stress.
It is another object of the invention to provide some structures that prevent formation of void by employing a high density passivation layer (HDP layer) which is formed by high density plasma.
It is a further object of the invention to provide some structures that are manufacturable.
In order to realize the objects of the invention, some structures are provided. These structures can be divided into two main categories:
First category, a low stress passivation layer is directly formed on a HDP layer.
Second category, a low stress layer is formed between passivation layer and HDP layer to reduce relative layer that between any two adjacent layers.
Therefore, possible structures of the invention comprise following varieties:
First, a low stress passivation layer is located between a passivation layer and a HDP layer.
Second, a lower stress passivation layer directly locates on a HDP layer.
Third, a low stress layer is formed between a passivation layer and a HDP layer.